In an arc welding machine, when generation of spatters increases, transpired metal adheres to the base metal to lower the welding quality. Also, when the spatter generation exceeds an allowable frequency, there is necessary an operation for correcting the welding part. If such correction is impossible, a member having such welding part must be scrapped, which lowers the efficiency of the welding operation as well as worsens cost performance greatly.
Conventionally, there have been proposed various methods in which spatters are reduced to thereby reduce the number of steps for correcting the welding part. For example, in JP-A-10-109163 publication, there is disclosed an output control method for carrying out constant current control in which a welding current value gradually decreasing after arc recurrence time is increased up to a high value after when a given time has passed from the arc recurrence time, thereby controlling the occurrence of a short circuit just after arc recurrence and thus reducing the generation of spatters.
Here, FIG. 4 shows a waveform of the current obtained when a welding operation is executed using the above-mentioned conventional output control method, in which the elapsed time is expressed on the horizontal axis and the welding current is expressed on the vertical axis. In FIG. 4, reference character 101 designates a short circuit period in which a wire and a base metal are short circuited with respect to each other, 102 an arc period in which an arc is generated between the wire and base metal, 103 an arc recurrence time when a short circuit is opened and an arc recurs, 104 a current just before arc recurrence, 105 an arc recurrence initial current, and 106 a constant current control period, respectively.
Next, description will be given below of the current waveform shown in FIG. 4 with reference to a control method for controlling the current with passage of time. In FIG. 4, there is shown constant current control in which the welding current value is gradually decreased by arc control until after passage of a given time starting from the arc recurrence time 103, whereas the welding current value is increased up to a high value after passage of the given time. The current value for execution of this constant current control, as shown in FIG. 4, is set for a value which does not exceed the current value just prior to arc recurrence, thereby being able to stabilize formation of droplets. After then, the constant current control 106 is stopped and the original arc control is resumed. By using such constant current control, a short circuit occurring just after arc opening can be controlled to thereby reduce the spatters.